This invention relates to a winding structure for a superconducting winding, and more specifically, this invention relates to the structure of a superconducting winding having cooling passages therein, and the method for making such a winding.
It is known that certain materials, known as superconductors, exhibit a complete loss of electrical resistance when cooled to a temperature approaching absolute zero. To maintain this zero resistance condition during use the superconductor must be maintained in the temperature range of about 0.degree.-10.degree. K. When a changing field current is applied to a superconducting coil, or when a three-phase winding experiences an unbalance of the three phases, or when residual magnetic flux penetrates the rotor electromagnetic shield following a cleared fault in a superconducting generator, heating of the coil occurs. Epoxy-impregnated superconducting windings can be made to adequately carry the critical current caused by any of the known sources of winding heating, so long as the current is changed slowly. In order to provide adequate margin for transient heating in the superconducting coil, the high current density capability of epoxy-impregnated windings cannot be fully utilized in prior art designs. If the coil could be made to accept rapidly changed current without heating of the coil, full utilization of the high current density capability of superconducting windings can be realized.
In the prior art techniques such as epoxy-impregnation have been used to secure the superconductor against motion. Cooling channels were added to the coils by inserting spacers having open channels into the coil prior to resin impregnation. For example, U.S. Pat. No. 3,983,427, issued Sept. 28, 1976 to Ulke discloses placing spacing elements 40 having channels 50 therein. These spacing elements are permanent parts of the winding and, therefore, decrease the ratio of superconductor per unit volume of the winding compared to the ratio for a fully potted coil (i.e., a coil having no cooling channels and having all spaces between superconductors completely filled with bonding material). This resulted in a coil having a substantially larger physical size than the fully potted winding having the same rating.
Therefore, one object of the invention is to provide a coil having adequate cooling channels to accommodate rapid changing of the field current in a coil substantially the same size as a fully potted coil of the same rating.
Another object is to provide a method of making a coil as described above.